1. Field of the Invention
This invention relates to a polymerisable fluid for the sealing and locking of engineering parts, particularly interfitting parts such as fasteners, more especially threaded fasteners such as nuts, bolts, screws, threaded nails and the like, or parts such as pipe joints which may be threaded or slip-fitted. It may be used in any circumstances of assembly of engineering parts where close tolerances obtain between adjacent surfaces of the parts.
2. Description of the Prior Art
The use of liquid or semi-liquid polymerisable substances for the purpose of sealing and locking interfitting parts is well known in the art. U.S. Pat. No. 3,489,599, describes an anaerobically polymerisable composition (particularly an acrylate monomer and a peroxide initiator) which is applied to at least one of the parts and which is covered with an envelope of oxygen-permeable material which is non-tacky. When the parts are assembled, oxygen is excluded and polymerisation occurs to seal the mating surfaces. U.S. Pat. No. 3,746,068 describes a pressure-activatable system based on encapsulated resin (particularly an epoxy resin) and a non-volatile curative therefor (preferably an amine), the capsules and curative being contained in a fluid binder which holds the system on an abutment surface of a mechanical fastener. The mixture dries to a tack-free film upon evaporation of solvent from the binder. Reference is also directed to U.S. Pat. No. 3,814,156 and British Patent 1,422,439.
U.S. Pat. No. 4,059,136 describes a thread locking system in which two physically separated deposits of fluid components of a polymerisable composition are applied to the threaded part, a reaction occurs at the contacting edges of the deposits to form a barrier which limits further reaction, and a cover coat is applied over both deposits, the cover coat being adapted to transform into a thin rupturable non-tacky film. When the threaded part is engaged with a mating body, the two deposits are intermixed and react to form a solid locking material.
Early locking compositions were applied in liquid form shortly before assembly of the interfitting parts. However, in order to facilitate the high rates of assembly of the mass-production engineering industries such as the automotive industry, pre-applied coatings are now preferred. These coatings are deposited on the fastener as dry to touch coatings in which polymerisable fluids are incorporated, one of the components generally being encapsulated and a binder being present to hold the polymerisable components in position on the part. The action of assembly causes fracture of the microcapsules and mixing of the components. This causes polymerisation of the fluids and locking and sealing of the assembly.
Although these pre-applied coatings have a number of advantages over liquid products in ease and speed of assembly, they have a number of shortcomings:
(a) The binder used is frequently not an integral part of the final polymerised film and the resultant strength is not as great as that of a film from the monomer alone, such as is obtained from a polymerisable liquid product, and very high strengths are not achievable.
(b) The film causes the friction of assembly to be increased, thus adversely affecting the torque/tension relationship so that the tension achievable in a fastener for a given torque is less than that achievable for an uncoated fastener.
(c) Stripping of the film can occur, particularly on some surfaces with ill fitting or burred nuts with consequent failure of the locking system.
(d) The coating is either deposited from organic solvent which is expensive and wasteful in operation and is normally a health and safety hazard, or is deposited from aqueous emulsion, but in this event ovens for drying are necessary which are expensive in capital requirements and in energy of operation.
It is an object of the present invention to provide a system of application of pre-applied coatings for sealing and locking threaded fasteners and other close fitting parts which does not suffer from the above-mentioned faults, and which gives coatings which are reliable and effective on a wide range of surfaces.
U.S. Pat. No. 4,325,985, issued after the priority date of the present application, describes a method in which a fluid material including an fluid resin is deposited on a threaded part and immediately thereafter, while the material is still fluid, a separate fluid film-forming cover coat is applied thereover and the cover coat is immediately transformed into a thin, solid, dry non-tacky film by brief exposure to radiation, such as ultra-violet radiation. The radiation-curable cover coat is cured through its depth and it does not participate in the subsequent cure on assembly of the fastener. The two systems involved in this method are two fluids and are physically separate. Therefore the procedure for coating the threaded member involves two steps.
It is a further object of the present invention to provide a system in which a single polymerisable fluid contains components adapted to form a dry coating thereon but to seal and lock one mechanical part to another upon assembly of the parts.